1. Field of the Invention
The present invention relates to a method of fabricating a system-on-chip and its structure. More particularly, the present invention relates to a method of fabricating a three-dimensional system-on-chip and its structure.
2. Description of Related Art
Due to competition in the market, embedding different integrated circuits such as ROMs, SRAMs, Flash memories, DRAMs, Logics, Digital circuits, and so on in a single chip is the current trend for manufacturing integrated circuits that are lightweight, small in size, and multi-functional, as required. This is called the system-on-chip (SOC). For example, embedded Flash memory is a circuit with a Flash memory and a Logic.
However, fabrication of DRAMs, Flash memories, Logics, radio frequency (RF) elements, etc. on a single chip makes the circuit layout design, which connects circuits to each other, relatively complicated. Moreover, manufacturing processes for elements having different functions are not the same; the complexity and the difficulty for fabrication of the system-on-chip, which has to integrate elements having different function on a single chip, are greatly increased. Therefore, the yield of the product is decreased and the production cost is increased.
It is therefore an objective of the present invention to provide a method of fabricating a three-dimensional system-on-chip. The method is described as follows. A first chip having a periphery circuitry region is provided, with a plurality of first contact pads formed in a surface of the periphery circuitry region. A second chip is then adhered on the first chip. The second chip includes a periphery circuitry region, with a plurality of second contact pads formed in a surface of the periphery circuitry region. Some of the second contact pads are aligned with some of the first contact pads. A plurality of first plugs is formed in the second chip, with some of the first plugs electrically connected to some of the first contact pads and some of the second contact pads. Then, a third chip is adhered on the second chip. The third chip includes a periphery circuitry region, with a plurality of third contact pads formed in a surface of the periphery circuitry region. Some of the third contact pads are aligned with some of the first plugs and some of the second contact pads. A plurality of second plugs is formed in the third chip, with some of the second plugs electrically connected to some of the second contact pads and some of the third contact pads. Also, some of the second plugs are electrically connected to some of the first plugs.
A three-dimensional system-on-chip structure comprises a plurality of chips and a plurality of plugs respectively fabricated in the chips. The chips are stacked on top of each other and each includes a periphery circuitry region. A plurality of contact pads is fabricated on each of the periphery circuitry regions. The plugs are formed in the corresponding stacked chips, and electrically connected to the corresponding contact pads of two of the corresponding chips which are adjacent to each other, or two of the corresponding chips which are not adjacent to each other.
Because each of the differently functioning chips is manufactured by its own manufacturing process, the complexity and the difficulty for the system-on-chip fabrication can be reduced. Therefore, the yield of the product is increased and the production cost is decreased. Moreover, a conventional interconnect process is employed for the electrical connections between the chips, the yield of fabricating the three-dimensional system-on-chip can be greatly increased. Furthermore, the differently functioning chips are not arranged on the same surface in the three-dimensional system-on-chip according to the present invention. Hence, the layout area required for the system-on-chip can be reduced. Also, the complexity and the difficulty for the circuitry layout design can be reduced. Even further, the chips are stacked on each other and connected through the plugs, so that signal transmission paths can be shortened and performance can be increased.